This invention relates to an envelope shape generation device in an electronic musical instrument and, more particularly, to an envelope shape generation device of an envelope shape memory system type.
In the art of envelope shape generation device, there have been proposed and used envelope shape generation devices of an envelope shape memory system type which prestore sampling shape values of envelope shapes as envelope shape data in envelope shape memories and these envelope shape data are read out in accordance with key-on and key-off operations.
These prior art envelope shape generation devices employ a tone color selection signal for reading out envelope shapes but it has been felt that these prior art devices are insufficient in naturalness of a tone produced.
When a natural musical instrument is played with, for example, a vibrato performance technique, there occurs the phenomenon that the envelope of a tone generated subtly changes in response to strength of the vibrato performance. In the prior art envelope shape generation devices, however, an envelope shape simulating such envelope of a natural musical instrument cannot be obtained.
It is, therefore, an object of the invention to provide an envelope shape generation device capable of generating a tone signal having an improved naturalness with a simple construction.
In the prior art envelope shape generation devices of the envelope shape memory system type, elements constituting respective portions of an envelope shape, i.e., an attack shape portion, loop shape portion and release shape portion etc., are stored in an envelope shape memory. Attack shape data of the attack shape portion is read out only once when a key-on operation has been made, then loop shape data of the loop shape portion is repeatedly read out until a key-off operation is made, and, when the key-off operation has been made, release shape data of the release shape portion is read out only once thereby to fade out the tone in accordance with the release shape.
In forming an envelope shape by these envelope shape generation devices, in the stage of reading loop shape data repeatedly by continuing a key-on operation, a key-off operation is made at any desired time point regardless of the state of reading of the loop shape data. This means that the reading of the loop shape is finished at any unexpected value within a range in which contents of the loop shape data and, therefore, an instantaneous value of the envelope shape, change during the key-on operation and, simultaneously, reading of the release shape is started.
For generating a release envelope shape from any value of a changing envelope value, it is conceivable to cause a head value of a release shape to agree with a mean value of a loop shape thereby to reduce discontinuity occurring in switching from the loop shape to the release shape. It is also conceivable to simply determine a head value of a release shape in correspondence to a fixed envelope shape value at the end of the loop shape data.
The former method, however, has the problem that a tremendous amount of data is required as release shape data. The latter method has the problem that a smooth connection of the envelope shape cannot be expected.
It is, therefore, another object of the invention to provide an envelope shape generation device which, in generating an envelope shape data having an improved naturalness, can always connect a loop shape and a release shape together smoothly by merely prestoring data for only one envelope shape as release shape data.